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The development of hybrid biofunctionalized nanomaterials has emerged as an attractive substitute for development of advanced biosensing platforms with superior synergistic properties. Herein, we report a label-free ultrasensitive electrochemical aptasensor comprising nanohybrid of graphene oxide (GO) and aptamer conjugated gold nanoparticles (GNP-A) for detection of cardiac biomarker Troponin I (TnI). The GNP-A are homogenously arranged by self-assembly on GO sheet to construct nanohybrid (GO@GNP-A) onto which the biomarker protein is analysed. TnI interactions at the aptamer biointerfaced nanohybrid surface causes electrochemical signal enhancement probed by using a redox active molecule. The consecutive increase in current signal is strongly attributed to conformational switching of aptamer and charge neutralization at the interface induced by TnI binding. The sensitivity of the nanohybrid aptasensor platform was found to be 0.001 pg/mL. The study has been further substantiated in Acute Myocardial Infarction (AMI) clinical samples for usage towards early, sensitive and efficient point-of-care detection of TnI.

Mycobacterium tuberculosis (Mtb) is a smart and successful pathogen since it can persist in the intimidating environment of the host by taming and tuning the immune system. Mtb releases MPT64 (Rv1980c) protein in high amounts in patients with active tuberculosis (TB). Consequently, we were curious to decipher the role of MPT64 on the differentiating dendritic cells (DCs) and its relation to evading the immune system. We observed that pre-exposure of differentiating DCs to MPT64 (DC

The manuscript highlights the efficacy of silver ions to act as a unique probe for the detection of bacterial contamination in water samples. The bacterial cell membrane adherence property of the silver ions was employed to develop two different bacterial detection assays employing colorimetric and electrochemical techniques. In one of the schemes, silver ion was used directly as a detector of bacteria in a colorimetric assay format, and in the other scheme surface-functionalized antibodies were used as a primary capture for specific detection of Salmonella enterica serovar Typhi. The colorimetric detection is based on silver-induced inhibition of urease activity and silver ion utilization by bacteria for the rapid screening of enteric pathogens in water. The specific detection of bacteria uses an antibody-based electrochemical method that employs silver as an electrochemical probe. The ability of silver to act as an electrochemical probe was investigated by employing Anodic Stripping Voltammetry (ASV) for targeted detection of Salmonella Typhi. For further insights into the developed assays, inductively coupled plasma mass spectrometry (ICP-MS) and transmission electron microscopy (TEM) studies were performed. The sensitivity of the developed assay was found to be 100 cfu mL−1 for colorimetric and 10 cfu mL−1 for electrochemical assay respectively.

Novel vaccination strategies are crucial to efficiently control tuberculosis, as proposed by the World Health Organization under its flagship program "End TB Strategy." However, the emergence of drug-resistant strains of Mycobacterium tuberculosis (Mtb), particularly in those coinfected with HIV-AIDS, constitutes a major impediment to achieving this goal. We report here a novel vaccination strategy that involves synthesizing a formulation of an immunodominant peptide derived from the Acr1 protein of Mtb. This nanoformulation in addition displayed on the surface a toll-like receptor-2 ligand to offer to target dendritic cells (DCs). Our results showed an efficient uptake of such a concoction by DCs in a predominantly toll-like receptor-2-dependent pathway. These DCs produced elevated levels of nitric oxide, proinflammatory cytokines interleukin-6, interleukin-12, and tumor necrosis factor-α, and upregulated the surface expression of major histocompatibility complex class II molecules as well as costimulatory molecules such as CD80 and CD86. Animals injected with such a vaccine mounted a significantly higher response of effector and memory Th1 cells and Th17 cells. Furthermore, we noticed a reduction in the bacterial load in the lungs of animals challenged with aerosolized live Mtb. Therefore, our findings indicated that the described vaccine triggered protective anti-Mtb immunity to control the tuberculosis infection.

An increase in antibiotic resistance has led to escalating the need for the development of alternate therapy. Antimicrobial peptides (AMPs) are at the forefront of replacing conventional antibiotics, showing slower development of drug resistance, antibiofilm activity, and the ability to modulate the host immune response. The ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) pathogens that jeopardize most conventional antibiotics are known to be involved in severe respiratory tract, bloodstream, urinary tract, soft tissue, and skin infections. Among them, S. aureus is an insidious microbe and developed resistance against conventional antibiotics. In the present study, an AMP (named as peptide-Ba49) isolated from Bacillus subtilis subsp. spizizenii strain from Allium cepa (the common onion) exhibited strong antibacterial efficacy against S. aureus ATCC 25923. The mode of action of this peptide-Ba49 on S. aureus was deciphered through various sensitive probes, i.e., DiSC3 (5) and H2DCFDA, suggesting the peptide-Ba49 to be acting upon through change in membrane potential and by triggering the production of reactive oxygen species (ROS). This induced disruption of the cell membrane was further supported by morphological studies using scanning electron microscopy (SEM). Investigations on a possible post-antibiotic effect (PAE) of peptide-Ba49 showed prolonged PAE against S. aureus. Furthermore, the peptide-Ba49 prevented the formation of S. aureus biofilm at low concentration and showed its potential to degrade the mature biofilm of S. aureus. The peptide-Ba49 also exhibited intracellular killing potential against S. aureus ATCC 25923 in the macrophage cells, and moreover, peptide-Ba49 was found to bolster the fibroblast cell migration in the scratch assay at low concentration, exhibiting a wound healing efficacy of this peptide. These studies demonstrated that peptide-Ba49 isolated from the strain B. subtilis subsp. spizizenii could be a therapeutic candidate to combat the pathogenic S. aureus infections.

Inspired by the interaction of colistin with lipopolysaccharides (LPS) of the bacterial outer membrane, we describe a simple, cost effective and rapid assay for the detection of bacterial contamination in water samples. Colistin, a bactericidal drug, has been used by us in a receptor configuration for detection of pathogenic microorganisms without involving any tedious sample preparation step. The approach employs the cationic antibiotic drug for dual purpose, firstly, as a primary binder for pathogens and secondly, as an aggregator for negatively charged Gold nanoparticles (GNPs). The former consists of colistin binding to bacteria in water that renders GNPs free in solution thus depicting red color and the latter shows colistin driven aggregation of GNPs producing blue colored solution. The assay works in a two-step procedure that involves addition of colistin and GNPs to the water sample before results can be visualized based on color change. The assay is sensitive at a concentration up to 10 bacterial cells·mL−1 in a time frame of 5 min without requiring any expensive reagents and instruments.

Rapid industrialization and innovative material processing routes have resulted in the contamination of natural resources. Qualitative and quantitative estimation of mercury in food, beverages, water sources, and other environmental media has become of prime importance for human well-being. The present healthcare sector desires cheap, easy to use, and portable field-based monitoring kits for the detection of hazardous pollutants like mercury. In view of these facts, there is a strong need for robust, cost effective, reproducible, ultrasensitive, selective, and portable technology for the detection of mercury in samples. Here, we report the facile direct redox sensing of mercury ions at the ppb level. In this work, a combined application of linear sweep voltammetry (LSV) and chronoamperometry techniques was made for the direct electrochemical sensing of mercury ions on a nanogold platform. This is the first report in which the direct electrochemical sensing of mercury is demonstrated based on LSV & chronoamperometry techniques without the use of any biomolecule/co-coordinating ligand. LSV works in one direction/sweep, thereby diminishing the possible occurrence of interfering agents in a reverse sweep. This new approach is more reliable, robust, ultrasensitive, and user friendly relative to previous methods. The fabricated Au/Nafion/GC electrode showed ultra-high sensitivity of 11.75 μA cm − 2 ppb − 1 [detection limit of 3.78 ppb (19 nM) with a linearity ranging up to 50 ppm] at a response time of

Herein, we demonstrate a facile and economic approach for colorimetric detection of microbial pathogens in drinking water, employing silver-urease interactions. In the presence of harmful pathogens, receptor coated silver nanoparticles (AgNPs) preferentially bind to the bacterial surface and urease catalytically elevates the pH of the solution, which is sensed by a pH responsive chromogenic dye. The assay demarcates bacterial contamination levels up to 102 cells mL-1 in a field-friendly method.

Herein, we report a new signal amplification scheme for quantitative biochemical analysis based on gold nanoparticle (GNPs) catalyzed polymerization of transparent silane solution to milky white and turbid siloxane. Using immunoassay as a proof of concept, GNP labeled immunoprobe was used to bind captured antigen and catalyse the polymerization reaction allowing sensitive biochemical investigation. The polymerization reaction was optimized for standard 96 well polystyrene microtiter plates and we discovered that sodium lactate acts as an enhancer in the polymerization reaction as it reduces detection time to merely 30 min. The sensing strategy was applied to detection and quantification of Salmonella Typhimurium in water and egg samples and the platform showed excellent visibly quantifiable analytical response up to 100 cells mL−1. Furthermore, clinical utility and potential of the method was validated by detecting Vi capsular polysaccharide (Vi antigen) responsible for typhoidal Salmonellosis in human serum in sandwich format with a detection limit of 1 ng mL−1. The method serves as the first report towards nanoparticle triggered polymerization for development of rapid and low cost quantitative biochemical assay.

A highly sensitive and robust polysilicon Field Effect transistor (SiFET) has been developed for the detection of an gold standard biomarker of myocardial infarction (AMI) Cardiac Troponin I (cTnI). This paper reports a polysilicon FET device integrated with a thin film of gold layer as a gate terminal which is biofunctionalized with specific cTnI binding single stranded DNA receptor aptamer to detect cTnI. The reported SiFET is fabricated using standard microfabrication unit processes. The detailed characterization of reported device is performed and thoroughly discussed at different stages of device development. The assessment of bio-interface is also studied using various surface characterization techniques such as Raman spectroscopy, Atomic force microscopy (AFM) and Contact angle measurements. The experimental results showed the significant response for cTnI concentration as low as 0.1 ng ml−1 for label free detection.

A novel approach for signal enhancement of electrochemical biosensors by incorporating mechanical vibrations has been developed. We report the electrochemical study of the ferricyanide and ferrocyanide Fe CN 6 − 3 / − 4 a redox couple, at room temperature (∼25 °C), under the effect of mechanical vibrations of different frequencies applied to the sensor, for sensitivity enhancement. The experimental results showed a sensitivity enhancement of ∼332% (from 3.125 nA μ M − 1 to 13.5 nA μ M − 1 ) at 88.75 Hz of vibration. This novel approach of signal sensitivity enhancement is also validated with antibody immobilization-based Vi antigen detection for typhoid assessment. The sensitivity enhancement up to ∼15% is achieved for Vi antigen detection under the mechanical vibration of 120 Hz. The sensor is fabricated using microfabrication technology. The vibration-assisted ultrasensitive biosensing platform is also prototyped as a portable and Internet of Thing (IoT) enabled device, suitable for point-of-care applications. Detailed features of the prototype along with the test results are elaborated in the paper.

The authors describe a method for detecting the pathogen S. typhimurium with a ‘yes-or-no’ kind of response. A fluorescein-tagged aptamer (Apt-FAM) probe was used for the specific recognition of pathogens, and molybdenum(IV) disulfide nanosheets (MoS2-Ns) were used as a primary binder of free (unbound) ssDNA that quenches its fluorescence. If, however, target pathogens are present, Apt-FAM probe binds to it and fluorescence is restored. The method displays a detection limit of 10 CFU·mL−1, is selective over E. coli and P. vulgaris, and therefore represents a promising on-site screening tool for microbes.

The precise and rapid diagnosis of malaria is key to prevent indiscriminate use of antimalarial drugs and help in timely treatment and management of the disease. This paper reports a label-free detection of P. falciparum infected red blood cells using a gold nanoparticle (GNP) enhanced platform. The GNPs were electrodeposited on screen-printed electrodes to form a well-controlled matrix that served the dual role of antibody immobilization and signal enhancement. The detection of infected red blood cells was carried out by measuring changes in electrical parameters as a result of its binding to cell reactive antibodies immobilized on the electrode. The assay showed good sensitivity and a linear response between the electron transfer resistance and the logarithm of the number of infected red blood cells which was observed over a concentration range of 102 cells per mL to 108 cells per mL. This is the first report where an antibody-functionalized electrochemical biosensing platform has been employed for the quantitative detection of P. falciparum infected whole red blood cells.

Combining synthetic macromolecules and biomolecular recognition units are promising in developing novel diagnostic and analysis techniques for detecting environmental and/or clinically important substances. Fluorescence resonance energy transfer (FRET) apta-immunosensor for explosive detection is reported using 2,4,6-trinitrotoluene (TNT) specific aptamer and antibodies tagged with respective FRET pair dyes in a sandwich immunoassay format. FITC-labeled aptamer was used as a binder molecule in the newly developed apta-immunoassay format where the recognition element was specific anti-TNT antibody labeled with rhodamine isothiocyanate. The newly developed sensing platform showed excellent sensitivity with a detection limit of the order of 0.4 nM presenting a promising candidate for routine screening of TNT in samples.

Specific immune detection of glycated hemoglobin is still a great challenge owing to the small epitopic difference between Hemoglobin (Hb) and HbA1c. We report a new electrochemical immunoassay format for point of care testing of HbA1c. A conducting self-assembled monolayer of mercaptophenyl boronic acid (MPBA) was used as a capture layer for binding of glycated proteins and ferrocene tagged anti-HbA1c antibody (FcAb) as a tracer molecule on a gold screen printed electrode. Validation of the new HbA1c assay was carried out using 6 clinical samples with known HPLC values and a correlation coefficient of 98 % was observed.

Highly luminescent water soluble CdTe quantum dots (QDs) were synthesized and conjugated with anti-HbA1c antibody to generate specific nanobioprobe. A sandwich immunoassay model was employed using capture HbA1c antibody as a specific receptor molecule and the QD-labeled secondary antibody as a dual (fluorescence cum electrochemical) tracer to quantify the concentration of HbA1c. A linear increase in current was observed for HbA1c analytical standards with a R(2) value of 0.990 and coefficient of variance ~5%. A comparison between HPLC and dual immunoassay for clinical samples showed a correlation coefficient of 89% and 96% for fluorescence and electrochemical detection methods respectively. The QD-based immunoassay shows great promise for rapid reproducible and cost effective analysis of HbA1c in clinical samples.

Binding of electron-deficient trinitrotoluene (TNT) to the electron rich amine groups on a substrate form specific charge-transfer Jackson-Meisenheimer (JM) complex. In the present work, we report formation of specific JM complex on amine functionalized reduced graphene oxide/carbon nanotubes- (a-rGO/CNT) nanocomposite leading to sensitive detection of TNT. The CNT were dispersed using graphene oxide that provides excellent dispersion by attaching to CNT through its hydrophobic domains and solubilizes through the available OH and COOH groups on screen printed electrode (SPE). The GO was reduced electrochemically to form reduced graphene that remarkably increases electrochemical properties owing to the intercalation of high aspect CNT on graphene flakes as shown by TEM micrograph. The surface amine functionalization of dropcasted and rGO/CNT was carried out using a bi-functional cross linker ethylenediamine. The extent of amine functionalization on modified electrodes was confirmed using energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS) and confocal microscopy. The FTIR and Raman spectra further suggested the formation of JM complex between amine functionalized electrodes and TNT leading to a shift in peak intensity together with peak broadening. The a-rGO/CNT nanocomposite prepared electrode surface leads to ultra-trace detection of TNT upto 0.01 ppb with good reproducibility (n=3). The a-rGO/CNT sensing platform could be an alternate for sensitive detection of TNT explosive for various security and environmental applications.

We report label-free detection of phenylurea herbicides by impedance spectroscopy using class specific anti-diuron antibodies. Gold nanoparticles (∼20 nm), used as signal enhancers cum immobilization matrix, were electrodeposited on carbon screen-printed electrodes (SPE) and functionalized with specific anti-diuron antibodies for the development of bio-interface. Faradic impedance spectroscopy was performed and changes in electrical parameters such as resistance to charge transfer (Rct) and capacitance of double layer (Cdl) were elucidated using Randles model for the equivalent circuit of the electrochemical cell. Rct parameter was used to draw the analytical inference and also for calculating the percentage cross reactivity of diuron antibody with various common analogues. The cross-reactivity was 397% with monuron, 64.2% with linuron and the least (22.9%) with fenuron. The diuron was detected in a label-free manner with a limit of detection equal to 5.46 ng mL−1. The observed response was linear in the useful analytic range of 1–1000 ng mL−1 for the standard diuron detection in water. The obtained results showed good promise for routine label-free monitoring of herbicides in environmental samples.

Photosynthetic bacterial reaction centers (BRC) have shown great potential for bioengineering applications. In the present work we demonstrate their preferentially oriented immobilization on top of a mercaptopropionic acid (MPA) self assembled monolayer (SAM) formed on gold screen printed electrodes (Au-SPE). The AFM of the self assembled biofilm reveals formation of nanohole features with the depths of 2.2–2.5 nm, consistent with the thickness of the BRC (~ 3 nm). Thus, BRCs organize into a sub-monolayer film on top of the MPA SAM layer. The square-wave voltammogram of the BRC films exhibits features due to the redox reactions for the bacteriochlorophyll dimer (the strongest), bacteriopheophytin, and the quinones (weak), indicating that the BRCs are more likely immobilized with the dimer side towards the electrode surface. Non-saturating illumination of the BRC film at open circuit conditions leads to a sharp spike of negative current which could be due to the electron acceptance by the oxidized dimer.

It has been already proved that electrical capacitance increases at the electrode surface due to binding of highly charged antigens on the biointerface. In this paper, this capacitance change was used to demonstrate a novel detection for cardiac troponin I (cTnI). Citrate-capped gold nanoparticles (GNPs) were deposited on screen printed electrodes using an innovative one-step electrochemical technique. The gold (Au) nanostructuration onto the electrode surface was characterized by atomic force and field emission scanning electron microscopies. The highly specific anti-cTnI antibodies were immobilized onto the Au matrix, and characterized by confocal microscopy. The interaction of cTnI with its corresponding antibody was studied with respect to electrical capacitance changes as deduced by using the Randles model of the equivalent circuit of the electrochemical cell. The sensor-to-sensor measurements error was registered less than 2% on the average measured capacitance. cTnI was successfully detected in a label-free manner with a limit of detection equal to 0.2 ng mL(-1). This obtained result was one order of magnitude better than that obtained with ELISA tests performed by using the same antibodies, with a detection limit of 4.3 ng mL(-1). (C) 2011 Elsevier B.V. All rights reserved.

The paper reports a highly sensitive enzyme free electrochemical immunoassay (EFEIA) for the detection of herbicide chlorsulfuron. The assay is based upon oxidative gold nanoparticle (GNP) dissolution in an acidic solution. The consequent release of large amounts of gold (Au) metal ions after dissolution of gold nanoparticles tagged to antibody leads to the development of sensitive stripping voltammetry based immunoassay. The detection is made possible by the reduction of Au3+ ions at the screen printed electrode surface followed by metal analysis by using the square wave voltammetry technique. The sensitivity of chlorsulfuron detection by competitive assay procedure was 6.7 pg mL−1 for EFEIA in marked contrast to optical detection using Standard ELISA procedure that gives a sensitivity of 4.97 ng mL−1. Keywords: Enzyme free, Electrochemical immunoassay, Gold nanoparticle, Chlorsulfuron detection

The efficacy of a Photosystem II (PS II)-based biosensor for the detection of explosive compounds has been explored. The idea is based on the close similarities in the chemical structures of the widespread explosives and herbicides, with the latter known to inhibit functioning of the PS II by attaching to the binding site of the QB mobile plastoquinone electron acceptor. The gold screen-printed electrodes (Au-SPE) functionalized with PS II-enriched particles were used for the detection of explosives in a droplet biosensor configuration. A crude preparation of PS II produced from spinach leaves, known as BBY particles, was employed to modify the Au-SPE working electrode employing BSA–glutaraldehyde-based immobilization procedure. Inhibition of the PS II functioning was detected by photo-electrochemical measurements in the presence of a mediator (either non-native quinone or ferricyanide). The biosensor was highly responsive to herbicides (as expected) as well as to picric acid, with limits of detection in the nanomolar range, but trace detection of trinitrotoluene (TNT) was not effective. The detection limit for picric acid was 25 nM as compared to ∼400 nM for TNT with duroquinone mediator. Low affinity of PS II to TNT has been corroborated by means of DCPIP assay; possible reasons for low affinity are discussed.

Label-free DNA detection plays a crucial role in developing point-of-care biochips. Capacitance detection is a promising technology for label-free detection. However, data published in literature often show evident time drift, large standard deviation, scattered data points, and poor reproducibility. To address these problems, mercapto-hexanol or similar alkanethiols are usually considered as blocking agents. The aim of the present paper is to investigate new blocking agents to further improve DNA probe surfaces. Data from AFM, SPR, florescence microscopy, and capacitance measurements are used to investigate new lipoate and ethylene-glycol molecules. The new surfaces offer further improvements in terms of diminished detection errors. Film structures are investigated at the nano-scale to justify the detection improvements in terms of probe surface quality. This study demonstrates the superiority of lipoate and ethylene-glycol molecules as blocking candidates when immobilizing molecular probes onto spot surfaces in label-free DNA biochip.

This paper investigates technological advancements in developing reliable technologies for label free detection of cancer markers. Capacitance detection was used successfully to develop an immunosensor. Rigorous probe immobilization was implemented to obtain reliable capacitance measurements. The commonly considered alkanethiols for proteins immobilization do not allow sufficiently stable capacitance measurements. Therefore, new ethylene-glycol functionalized alkanethiols were used as more suitable materials to develop lab-on-a-chip detection of cancer markers. Results from AFM, Chemi-luminescence, Fluorescence, Cyclic Voltammetry, QCM, and capacitance measurements showed that three (ethylene-glycol) alkanethiols highly stabilized the sensing surfaces in time. The measured capacitance on the antibody layers was in the range of 60–70 nF/cm2 and 80–115 nF/cm2 for the antigen detection. The developed system was utilized to detect the Hepatocarcinoma marker SCCA, and the whole IgM fraction from Hepatocarcinoma patient’s serum. Electrode by electrode reproducibility within the same chip increased by one order of magnitude (variations were reduced from 30–40% down to less than 2%) using these new alkanethiols, while the reached limit in sensitivity was close to 2.43 μg/ml.

Improved label-free capacitive detection was very recently demonstrated for both ssDNA and antigen target molecules. That improvement is due to ethylene-glycol alkanethiols monolayers used as linkers for anchoring probe molecules. The presence of ethylene-glycol chains into the thin films greatly reduces time drift, detection error, and non-specific signals. It also increases ideality of the electrochemical interface behavior. However, the ideality of probe surfaces is partially lost when dealing with antibodies. The aim of this paper is to show this loss of ideality by means of capacitance measurements upon the frequency as acquired in label-free detection of cancer markers.

DNA, the blueprint of life, has taken centre stage in biological research during the past few decades. The elucidation of the molecule's structure 50 years ago and the unravelling of the genetic code revolutionized the field of biotechnology. They sparked the creation of whole new industries based on this knowledge and on the various tools and technologies that have subsequently developed. Biologically, the well‐known function of DNA is to code for functional proteins that are the expressed form of hereditary, genetic information. But in the past few years, the discovery that DNA can conduct an electrical current has made it an interesting candidate for other roles that nature did not intend for this molecule. In particular, DNA could be useful in nanotechnology for the design of electric circuits, which could help to overcome the limitations that classical silicon‐based electronics is facing in the coming years. In general, DNA electronics does not aim to make something new. Its immediate goal is to improve old concepts in a new manner, although in the process it may create entirely new ideas in nanoelectronics. This field is highly interdisciplinary, merging physics, biology, chemistry, computer science, engineering and so on, to use individual DNA molecules for producing a new range of electronic devices that are much smaller, faster and more energy efficient than the present semiconductor‐based electronic devices. The basic unit of an integrated circuit, such as a computer processor or a memory chip, is the transistor, a simple electronic switch that is etched into various layers of silicon. Alien atoms, added during the production process, allow a transistor to switch between a conducting and a non‐conducting state, hence the name ‘semiconductor’. A modern microprocessor, such as the Pentium IV® chip, has more than 40 million transistors on a silicon chip that is only slightly …

A large improvement of the electrochemical capacitive detection of ssDNA and antigens by using ethylene-glycol alkanethiol monolayers has been recently demonstrated. Alkanethiol monolayers without ethylene-glycol functionalization do not show the required electrochemical stability. In this paper, we demonstrate that both phenomena are related to their morphological structure at nano-scale. Ethylene-glycol monolayers were compared with similar films without ethylene-glycol function. Capacitance measurements were used to verify the improved capacitance stability of the electrochemical interface. AFM images were used to investigate films packing and morphology at the nano-scale. This letter demonstrates that films without ethylene-glycol segment present deep grooves which are related to electrochemical instability while the improvement in case of ethylene-glycols is due to the absence of such a feature. (C) 2009 Elsevier B.V. All rights reserved.

Specific nucleic acid aptamers using the microtiter plate based modified SELEX method against explosive trinitrotoluene are reported. Efficient partitioning of dsDNA was carried out using streptavidin labeled gold nanoprobes for the selection of specific aptamers. The selected binders having an affinity of ~10(-7) M were used in the newly developed electrochemical aptasensor, exhibiting a detection limit of around 1 ppb for trinitrotoluene.

We report lithium ion intercalation mediated efficient exfoliation of graphite to form monolithic graphene sheets which have subsequently been investigated for the development of highly sensitive label-free electrochemical detection platform for cardiac biomarker, Troponin I (cTnI). The spectroscopic and morphological analysis demonstrated the formation of defect free graphene sheets which were successfully employed to fabricate an inter-digited microdevice in a drain-source configuration on a silicon biochip. The graphene gated biochip functionalized with anti-cTnI antibodies used in label free detection of cTnI which exhibited an excellent sensitivity in the picogram range (~1 pg mL(-1)) for cTnI without the use of any enzymatic amplification that promises its potential applicability for bio-molecular detection in clinical diagnosis.

Graphene and related materials have come to the forefront of research in electrochemical sensors during recent years due to the promising properties of these nanomaterials. Further applications of these nanomaterials have been hampered by insufficient sensitivity offered by these nanohybrids for the type of molecules requiring lower detection ranges. Here, we report a signal amplification strategy based on magneto-electrochemical immunoassay which combines the advantages of carbon nanotube and reduced graphene oxide together with electrochemical bursting of magnetic nanoparticles into a large number of metal ions. Sensitive detection was achieved by precisely designing the nanohybrid and correlating the available metal ions with analyte concentration. We confirmed the ultrahigh sensitivity of this method for a new generation herbicide diuron and its analogues up to sub-picomolar concentration in standard water samples. The novel immune-detection platform showed the excellent potential applicability in rapid and sensitive screening of environmental pollutants or toxins in samples.

Photosynthetic reaction centers were immobilized onto gold screen-printed electrodes (Au-SPEs) using a self-assembled monolayer (SAM) of mercaptopropionic acid (MPA) which was deliberately defective in order to achieve effective mediator transfer to the electrodes. The pure Photosystem II (PS II) cores from spinach immobilize onto the electrodes very efficiently but fair badly in terms of photocurrent response (measured using duroquinone as the redox mediator). The cruder preparation of PS II known as BBY particles performs significantly better under the same experimental conditions and shows a photocurrent response of 20-35 nA (depending on preparation) per screen-printed electrode surface (12.5mm(2)). The data was corroborated using AFM, showing that in the case of BBY particles a defective biolayer is indeed formed, with grooves spanning the whole thickness of the layer enhancing the possibility of mass transfer to the electrodes and enabling biosensing. In comparison, the PS II core layer showed ultra-dense organization, with additional formation of aggregates on top of the single protein layer, thus blocking mediator access to the electrodes and/or binding sites. The defective monolayer biosensor with BBY particles was successfully applied for the detection of photosynthesis inhibitors, demonstrating that the inhibitor binding site remained accessible to both the inhibitor and the external redox mediator. Biosensing was demonstrated using picric acid and atrazine. The detection limits were 1.15 nM for atrazine and 157 nM for picric acid.

A disposable electrochemical immunosensor has been developed for the determination of phenyl urea herbicide-diuron using a low cost laser ablated gold electrodes (LC-LAGE) fabricated on polystyrene substrate. The electrodes were electrochemically deposited with prussian blue-gold nanoparticle (PB-GNP) film, and a competitive inhibition immunoassay was performed on LC-LAGE by using a specific hapten-protein conjugate. The binding of available diuron specific antibody on conjugate coated electrode was detected using alkaline phosphatase rabbit anti-IgG antibody. The addition of 1-naphthyl phosphate substrate resulted in the production of electrochemically active product, 1-naphthol, which was monitored using square wave voltammetry technique. The assay exhibited an excellent sensitivity and specificity showing the dynamic response range between 1 ppt and 10 ppm for diuron with detection limit around 1 ppt. This study provides insight into development of a rapid and high-throughput screening of pesticides in environmental samples at a very low cost.

Label-free DNA detection is of crucial role to when developing point-of-care biochips to be used in personalized therapy. Capacitance detection is a promising technology for label-free DNA detection. However, data published in literature often show evident time drift, large standard deviation, scattered data points, and poor reproducibility. To solve these problems, alkanethiol molecules such as mercapto-hexanol are usually considered as blocking agents. The aim of the present paper is to investigate new blocking agents to further improve DNA probe surfaces. Data from AFM, SPR, fluorescence microscopy, and capacitance measurements are used to demonstrate the new lipoates molecules. Moreover precursor layers obtained by using Ethylene-glycol alkanethiols offer further improvements in terms of diminished detection errors. Film structure is investigated at the nano-scale to justify the detection improvements in terms of probe surface quality. This study demonstrates the superiority of lipoate and Ethylene-glycol molecules as blocking candidates when immobilizing molecular probes onto spot surfaces in label-free DNA biochip.

During the last half century the electronic components and computers have grown more and more powerful with theshrinking dimensions of transistors which is approaching 100nm with about a billion tiny devices working togetheron a single processor. The laws of quantum mechanics and limitations of materials and fabrication techniquesrestrict further reduction below 100nm. The most promising area is Biomolecular Electronics concerning design andfabrication of basic electronic components using biomolecules. Various organic polymers are being studied forvisualization of individual molecular electronic wires and diode switches but we see enormous potential in use ofDNA for such devices due to its inherent characteristics. This is because DNA can act as insulator semiconductor,conductor or superconductor depending upon the base sequence, length and orientation. The DNA can be coatedselectively with metals with molecular level precision giving us capability to design molecular electroniccomponents, such as, diode, triode, transistor, etc.This paper discusses the DNA based language developed by our group for coding and decoding any digitalinformation in terms of DNA sequence. Basic arithmetical operations, such as, addition subtraction, multiplication,division and exponential have been defined in terms of DNA sequence and their validity has been demonstrated.Paper will also discuss our programme on study of DNA electrical behaviour in terms of sequence; length andorientation for development of biomolecular electronic components and for understanding DNA damaged chemistry. The principles of physics, as far as I can see, do not speak against the possibility of maneuvering things atom byatom. It is not an attempt to violate any laws; it is something, in principle that can be done; but in practice, it hasnot been done because we are too big.You would be able to write the entire Encyclopedia Britannica on the head of a pin, with huge amounts of room tospare. You would be able to build miniature machines so small that they could manipulate at a nearly molecularscale. And you would be able to build things, atom by atom."Nobel Laureate Richard Feynman INTRODUCTIONDuring the last few years interest in molecular and self-assembled devices is growing fast to over come thelimitation of semiconductor integrated circuits and sensors. This is because semiconductor devices are approachinglimits in terms of speed and miniaturization. So we have to look for entirely new concepts. Number of approacheshave been explored e.g. quantum devices, single electron devices, carbon nanotubes and molecular devices etc. the

A solid phase extraction micro-cartridge containing a non-polar polystyrene absorbent matrix was coupled with an electrochemical immunoassay analyzer (EIA) and used for the ultra-sensitive detection of the phenyl urea herbicide diuron in real samples. The EIA was fabricated by using carboxylated carbon nanotubes (CNTs) functionalized with a hapten molecule (an amine functionalized diuron derivative). Screen printed electrodes (SPE) were modified with these haptenized CNTs and specific in-house generated anti diuron antibodies were used for bio-interface development. The immunodetection was realized in a competitive electrochemical immunoassay format using alkaline phosphatase labeled secondary anti-IgG antibody. The addition of 1-naphthyl phosphate substrate resulted in the production of an electrochemically active product, 1-naphthol, which was monitored by using differential pulse voltammetry (DPV). The assay exhibited excellent sensitivity and specificity having a dynamic response range of 0.01 pg mL(-1) to 10 μg mL(-1) for diuron with a limit of detection of around 0.1 pg mL(-1) (n = 3) in standard water samples. The micro-cartridge coupled hapten-CNTs modified SPE provided an effective and efficient electrochemical immunoassay for the real-time monitoring of pesticides samples with a very high degree of sensitivity.

Sensing systems based on electrochemical detection have generated great interest because electronic readout may replace conventional optical readout in microarray. Moreover, they offer the possibility to avoid labelling for target molecules. A typical electrochemical array consists of many sensing sites. An ideal microfabricated sensor-chip should have the same measured values for all the equivalent sensing sites (or spots). To achieve high reliability in electrochemical measurements, high quality in functionalization of the electrodes surface is essential. Molecular probes are often immobilized by using alkanethiols onto gold electrodes. Applying effective cleaning methods on the chip is a fundamental requirement for the formation of densely-packed and stable self-assembly monolayers. However, the available well-known techniques for chip cleaning may not be so reliable. Furthermore, it could be necessary to recycle the chip for reuse. Also in this case, an effective recycling technique is required to re-obtain well cleaned sensing surfaces on the chip. This paper presents experimental results on the efficacy and efficiency of the available techniques for initial cleaning and further recycling of micro-fabricated chips. Piranha, plasma, reductive and oxidative cleaning methods were applied and the obtained results were critically compared. Some interesting results were attained by using commonly considered cleaning methodologies. This study outlines oxidative electrochemical cleaning and recycling as the more efficient cleaning procedure for electrochemical based sensor arrays. (C) 2009 Elsevier B.V. All rights reserved.